Effect of Inoculum Pretreatment on the Composition of Microbial Communities in Anaerobic Digesters Producing Volatile Fatty Acids

Abstract

Volatile fatty acids (VFAs) are intermediates in the methane formation pathway of anaerobic digestion and can be produced through the fermentation of organic wastes. VFAs have become an anticipated resource- and cost-effective way to replace fossil resources with higher added value and more versatile fuels and chemicals. However, there are still challenges in the production of targeted compounds from diverse and complex biomasses, such as urban biowastes. In this study, the aim was to modulate the microbial communities through inoculum treatment to enhance the production of green chemicals. Thermal and freeze-thaw treatments were applied to the anaerobic digester inoculum to inhibit the growth of methanogens and to enhance the performance of acidogenic and acetogenic bacteria. VFA fermentation after different inoculum treatments was studied in batch scale using urban biowaste as the substrate and the process performance was assessed with chemical and microbial analyses. Inoculum treatments, especially thermal treatment, were shown to increase VFA yields, which were also correlating with the dynamics of the microbial communities and retention times of the test. There was a strong correlation between VFA production and the relative abundances of the microbial orders Clostridiales (families Ruminococcaceae, Lachnospiraceae and Clostridiaceae), and Lactobacillales. A syntrophic relationship of these taxa with members of the Methanobacteriales order was also presumed.

Optimization of the Process of Methane Production From Wheat Straw and Bovine Manure Co-Digestion by Ultrasound Disintegration and Physicochemical Treatments

“…In the second step of AD (5 th -6 th day) we observed an increase in pH value to 7.3 for BM and 6.9 for SS and diminution of VFAs to 0.8 for BM and 1.8 g/L for SS. This complies with the results obtained by Blasco et al [41]. This is explained by the value buffer of pH and the consumption of the VFAs by bacteria [42].…”

“…The last step (5 th -6 th day) shows the stabilization of biogas production and the end of the methane, The accumulation of hydrogen develops significant pressure which blocks the activity of acetogenic bacteria that stop acetate production. Due to the symbiotic relation between acetogenic and methanogenic bacteria, these latter utilize this hydrogen in methane production and significant hydrogen pressure does not occur [38][39][40][41][42][43][44][45].…”

Effects of Bacillus subtilis and Bacillus licheniformis on growth performance, immunity, short chain fatty acid production, antioxidant capacity, and cecal microflora in broilers

“…Moreover, research has indicated that B. subtilis can induce a shift toward butyrate-producing bacteria in the broiler gut microbiome ( Jacquier et al., 2019 ), which was consistent with our results. Per the outcome of LEfSe higher levels of bacteria associated with the production of SCFAs, such as the unclassified_f_Lachnospiraceae, g_Ruminococcus , and g_Faecalibacterium , amongst others ( Antonissen et al., 2016 ; Blasco et al., 2020 ), were detected after B. subtilis or B. licheniformis supplementation. Considering these combined results, it may explain the significant increase in level of the SCFAs.…”

Effects of Rhamnolipids on Growth Performance, Immune Function, and Cecal Microflora in Linnan Yellow Broilers Challenged with Lipopolysaccharides

“…Bacteroides are known to be major producers of branched-chain amino acids, acetic acid, and butyric acid [ 49 , 50 ]. In addition, the most abundant phyla involved in the fermentation of glucose were Firmicutes , Bacteroidetes , and Proteobacteria, of which especially Firmicutes (genus Clostridium ) were connected to the highest production of SCFAs [ 51 ]. Firmicutes are known to produce butyrate and other SCFAs to maintain intestinal health by suppressing inflammation and providing energy to enterocytes [ 52 , 53 ].…”